Process for removal of oxygenates from a paraffin stream

ABSTRACT

The present invention comprises a process for removal of oxygenates from a paraffin-rich or olefin-rich paraffin stream which comprises passing a feed stream, comprising one or more C 10  to C 15  feed paraffins or C 10  to C 15  olefin-rich paraffin stream and one or more oxygenates through an adsorbent bed comprising one or more adsorbents selected from silica gel, activated alumina and sodium x zeolites to remove essentially all of said oxygenates; and recovering said paraffins. A second adsorbent bed may be employed to more thoroughly remove these oxygenates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of application Ser. No.10/739,765 filed Dec. 18, 2003 now abandoned, which in turn is aContinuation-In-Part of application Ser. No. 10/318,599 filed Dec. 12,2002, now abandoned, the contents of both which are hereby incorporatedby reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to a process for removing oxygenates fromparaffins or paraffin and olefin mixture. This invention is inparticular useful in removal of oxygenates from C₁₀ to C₁₅ paraffins ora mixture of paraffins and olefins prior to use of these paraffins orolefins or mixtures thereof in further processes or reactions.

There are a number of industrial applications for paraffins or olefinsor mixtures thereof in the C₁₀ to C₁₅ range. Among these uses are as aprecursor to linear alkylbenzene benzene (LAB) which is used to producelinear alkylbenzene sulfonate (LAS), the workhorse surfactant of thedetergent industry. These paraffins or olefins or mixtures thereof canalso be used as precursors to be upgraded to higher value fuels. Asconcerns over pollution caused by traditional fossil fuels increase andas sources of crude oil decrease, there has been increased interest inother sources of energy. One promising source of energy is the syntheticproduction of fuels, lubricants and other products from natural gas orcoal. The gas to fuels process is often referred to as gas-to-liquids orGTL and is often made by the Fischer-Tropsch process. See for example,U.S. Pat. No. 4,973,453, which is incorporated by reference herein. Thelinear paraffins and olefins in the C₁₀ to C₁₅ range are of particularvalue in connection with these processes.

The synthetic production of hydrocarbons by the catalytic reaction ofsynthesis gas is well known and is generally referred to as theFischer-Tropsch reaction. The Fischer-Tropsch process was developed inearly part of the 20^(th) century in Germany. It was practicedcommercially in Germany during World War II and later has been practicedin South Africa.

Synthesis gas (primarily hydrogen and carbon monoxide) is produced fromcoal or natural gas (methane). Then the synthesis gas is converted toliquid hydrocarbons. The Fischer-Tropsch reaction for convertingsynthesis gas has been characterized in some instances by the followinggeneral reaction:

The hydrocarbon products derived from the Fischer-Tropsch reaction rangefrom some methane to high molecular weight paraffinic waxes containingmore than 50 carbon atoms.

Numerous catalysts incorporating active metals, such as iron, cobalt,ruthenium, rhenium, etc. have been used in carrying out the reaction andboth saturated and unsaturated hydrocarbons can be produced. Thesynthesis reaction is very exothermic and temperature sensitive wherebytemperature control is required to maintain a desired hydrocarbonproduct selectivity.

The synthesis gas used in the Fischer-Tropsch reaction may be made fromnatural gas, gasified coal and other sources. A number of basic methodshave been employed for producing the synthesis gas (“syngas”) utilizedas feedstock in the Fischer-Tropsch reaction. The numerous methodologiesand systems that have been used to prepare synthesis gas include partialoxidation, steam reforming, auto-reforming or autothermal reforming.Both fixed and fluid bed systems have been employed.

The reforming reactions are endothermic and a catalyst containing nickelis often utilized. Partial oxidation (non-catalytic or catalytic)involves sub-stoichiometric combustion of light hydrocarbons such asmethane to produce the synthesis gas. The partial oxidation reaction istypically carried out commercially using high purity oxygen.

In some situations these synthesis gas production methods may becombined to form another method. A combination of partial oxidation andsteam reforming, known as autothermal reforming, wherein air may be usedas the oxygen-containing gas for the partial oxidation reaction has alsobeen used for producing synthesis gas heretofore. Autothermal reforming,the combination of partial oxidation and steam reforming, allows theexothermic heat of the partial oxidation to supply the necessary heatfor the endothermic steam reforming reaction. The autothermal reformingprocess can be carried out in a relatively inexpensive refractory linedcarbon steel vessel whereby a relatively lower cost is typicallyinvolved.

The Fischer-Tropsch process to produce paraffins and paraffin/olefinmixtures also produces a wide variety of oxygenates. These oxygenates,which include aldehydes, acids, ketones and alcohols, are detrimental ina variety of applications of these paraffins or olefins or mixturesthereof. In particular, the catalysts used to further process theparaffins and paraffin/olefin mixture to their desired end product arepoisoned by oxygenates. The oxygenate content needs to be reduced fromamounts on the order of about 200 to 400 parts per million in anuntreated paraffin/and (or) olefins stream, down to as low as 1 part permillion or lower in order for the paraffins or olefins or mixturesthereof to be processed without poisoning the adsorbent/catalyst orotherwise being detrimental in the processing of these paraffins orolefins or mixtures thereof.

There have been several different adsorption schemes proposed forremoval of oxygenates from low carbon paraffins, i.e. those averagingabout C₅. For example, in U.S. Pat. No. 6,111,162, hydrocarbons with 3to 8 carbon atoms were treated by removal of oxygenated contaminants byan adsorbent comprising silica gel. In U.S. Pat. No. 5,427,689, avariety of polar substances, including water, alcohols, ethers,aldehydes, ketones, amines, mercaptans, organic sulfides and carboxylicacids were removed from a hydrocarbon containing 1 to 10 carbon atomsusing a sorbent composition comprising aluminum borate and zirconiumborate. However, heretofore, there has not been proposed a process forsufficiently removing oxygenates from the high carbon (C₁₀ to C₁₅)paraffins and paraffin/olefin mixture employed in the process of thepresent invention. These mixtures comprise from 0 to 50 wt-% olefins and50 to 99.99 wt-% paraffins. There are often dozens of differentoxygenate compounds found in a paraffin and paraffin/olefin mixture feedmade by the Fisher-Tropsch process and it is necessary to have a generalprocess that works to remove all the oxygenate species in order to makeuse of the paraffins and paraffin/olefin mixture in a wide variety ofprocesses. Accordingly, it is the combined presence of these compoundsthat it is considered desirable to remove from the paraffin andparaffin/olefin mixture feed. In addition, in many applications of thepresent invention, it is desirable to be able to regenerate theadsorbents used to remove oxygenates from the paraffin andparaffin/olefin mixture feed. There are considerable cost savings inbeing able to reuse the adsorbents after regeneration of the bed, ratherthan frequent bed replacement.

SUMMARY OF THE INVENTION

The present invention comprises a process for removal of oxygenates froma stream comprising 50 to 99.99 wt-% paraffins and 0 to 50 wt-% olefinscomprising passing a feed stream, comprising one or more C₁₀ to C₁₅ feedparaffins and olefins mixture and one or more oxygenates through anadsorbent bed to remove essentially all of the oxygenates; andrecovering the paraffins and the olefins, when present. The level ofoxygenates is below the level that is detectable with standardlaboratory procedures, such as gas chromatography. In some embodimentsof the present invention, it is considered necessary to send theparaffin-rich stream through a second adsorbent bed comprising amolecular sieve in order to insure completion of removal of theoxygenate impurities. Typically, a 5A polishing bed is used to completetheir removal from the paraffin-rich stream. This invention isparticularly useful in purifying the feed streams for certain reactions.Trace amounts of oxygenates can have detrimental effects upon anadsorbent/catalyst. Among the processes that are improved by the removalof oxygenates in accordance with the present invention are thedehydrogenation of normal paraffins to olefins and processes forseparating normal paraffins from branched and cyclic hydrocarbons. Inthe case where the feed is a mixture of paraffins and olefins, thisstream is suitable for direct alkylation with benzene after oxygenateremoval treatment prior to forming alkylated benzene. Accordingly, oneembodiment of the present invention comprises a process fordehydrogenation of normal paraffins to olefins comprising first passinga paraffin stream comprising C₁₀ to C₁₅ paraffins through at least oneadsorbent bed comprising one or more adsorbents selected from the groupconsisting of silica gel, activated alumina and alkaline or alkalineearth cation exchange X-zeolite wherein the adsorbents removeessentially all oxygenates from the paraffin stream by adsorption, andthen passing the paraffin stream to a reactor containing adehydrogenation catalyst to convert at least a portion of the paraffinstream to olefins. Another embodiment of the present invention comprisesa process comprising first passing a paraffin stream comprising C₁₀ toC₁₅ paraffins through at least one adsorbent bed comprising one or moreadsorbents selected from the group consisting of silica gel, activatedalumina and alkaline or alkaline earth cation exchange X-zeolite whereinthe adsorbents remove essentially all oxygenates from the paraffinstream by adsorption, and then passing the paraffin stream to anadsorbent bed comprising a molecular sieve to separate n-paraffins fromthe paraffin stream.

Another embodiment of the present invention comprises a processcomprising of first passing the stream comprising 50 to 99.99% C₁₀ toC₁₅ paraffins and 0 to 50% olefins through at least one adsorbent bedcomprising one or more adsorbents selected from the group consisting ofsilica gel, activated alumina and alkaline or alkaline earth cationexchange X-zeolite wherein the adsorbents remove essentially alloxygenates from the stream by adsorption, and then combining the streamwith benzene and passing the resulting alkylation stream to a reactorcontaining a alkylation catalyst to convert at least a portion of theolefins to alkylated benzene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a feed breakthrough in alumina adsorbent of 1000 ppm eachof 2-undecanone, 2-undecanol, decyl alcohol, lauric acid, and2-dodecanol.

FIG. 2 shows a feed breakthrough in a silica gel adsorbent of 1000 ppmeach of 2-undecanone, 2-undecanol, decyl alcohol, lauric acid, and2-dodecanol.

FIG. 3 shows a feed breakthrough in a different silica gel adsorbent of1000 ppm each of 2-undecanone, 2-undecanol, decyl alcohol, lauric acid,and 2-dodecanol.

FIG. 4 shows a feed breakthrough of a 13× adsorbent of 1000 ppm each of2-undecanone, 2-undecanol, decyl alcohol, lauric acid, and 2-dodecanol.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a process for removal of oxygenates froma paraffin and olefin mixture or a paraffin-rich stream which comprisespassing a feed stream, comprising one or more C₁₀ to C₁₅ feed paraffinsor paraffin and olefin mixture and one or more oxygenates through anadsorbent bed to remove essentially all of the oxygenates; andrecovering the paraffins or paraffin and olefin mixture. Typically, theparaffin and olefin mixture referred to herein as olefin-rich streamswill comprise up to 50 wt-% olefin with the remainder comprisingparaffins, plus impurities. Up to 1% of the paraffin and olefin mixtureor paraffin-rich streams will comprise the oxygenate impurities to beremoved by the present invention. In the paraffin-rich streams, thestreams typically comprise about 99 wt-% paraffins and sometimes up to99.99 wt-% paraffins. In such a typical paraffin-rich or olefin-richparaffin stream produced in a gas to liquid Fisher-Tropsch process, ithas been found that numerous hydrocarbon oxygenates are produced,including alcohols, aldehydes, ketones and acids. It is necessary to usea process to remove virtually all the oxygenates in order to employthese paraffins or olefin-rich paraffins without poisoning theadsorbent/catalyst that is used in such processes as conversion ofparaffins to olefins, alkylation of olefins with benzene, and inseparation of n-paraffins from other paraffins. Table 1 illustrates theextensive list of oxygenates found in three samples of paraffins orolefin-rich paraffins prior to treatment by the process of the presentinvention, all of which are removed by the process of the presentinvention. All numbers are in parts per million.

TABLE 1 Compound Feed 1 Feed 2 Feed 3 1-Nonanol 1.6 12.1 3.6 2-Nonanol<0.4 1.6 1.8 1-Decanol 2.2 14.0 12.1 2-Decanol 0.4 4.5 3.3 3-Decanol<0.4 <0.4 9.2 4-Decanol 0.3 4.2 3.1 Unk C10 Alcohols <0.4 <0.4 <0.41-Undecanol 1.6 9.0 4.3 2-Undecanol 1.4 4.5 3.9 3-Undecanol 0.9 3.3 4.84-Undecanol 0.6 2.1 5.2 Unk C11 Alcohols 0.8 3.2 5.7 1-Dodecanol 0.5 1.01.4 2-Dodecanol 4.6 8.0 <0.4 Unk C12 Alcohols 6.0 15.3 <1.0 1-Tridecanol<0.4 <0.4 <0.4 Unk C13 Alcohols 3.1 6.7 <0.4 1-Tetradecanol <0.4 <0.4<0.4 Unk C14 Alcohols 1.0 0.5 <0.4 1-Octanal 4.5 4.9 4.3 1-Nonanal 4.26.7 7.7 1-Decanal 3.9 8.3 16.9 1-Undecanal 3.0 7.2 17.1 1-Dodecanal <0.61.4 <1.0 1-Tridecanal <0.5 <0.5 <1.0 2-Heptanone 0.7 1.6 <0.4 2-Octanone1.5 3.8 <0.4 2-Nonanone 2.4 6.6 0.6 2-Decanone 3.1 10.1 2.9 2-Undecanone3.3 11.3 3.5 2-Dodecanone 1.6 5.7 1.0 Unk C11 Ketones 2.2 1.0 5.2 UnkC12 Ketones 1.3 5.4 6.1 Butanoic Acid 3.3 1.2 1.6 Pentanoic Acid 6.7 2.41.6 Hexanoic Acid 10.4 3.6 3.3 Heptanoic Acid 12.8 4.5 4.3 Octanoic Acid14.3 4.7 6.7 Nonanoic Acid 16.0 5.3 9.4 Decanoic Acid 16.7 5.1 10.1Undecanoic Acid 12.0 4.0 15.4 Lauric Acid 6.6 2.4 12.6

Table 2 shows a summary of the types of oxygenates found in the feed.

TABLE 2 Compound Feed 1 Feed 2 Feed 3 Alcohols 25.0 90.0 58.4 Aldehydes15.6 28.5 46.0 Ketones 12.6 39.1 8.0 Acids 98.8 33.2 65.0

In the practice of the present invention, a paraffin-rich or olefin-richparaffins stream is first passed though an adsorbent bed containing atleast one adsorbent selected from the group consisting of silica gel,activated alumina and alkaline or alkaline earth cation exchangeX-zeolite. The X-zeolite has a Si/Al₂ ratio from about 2.0 to 3.0. AnX-zeolite having a Si/Al₂ ratio of 2, 2.3 or 2.5 is preferred.

In addition to removal of oxygenates, in some embodiments of the presentinvention, it is necessary to remove compounds containing other elementsfrom Group VIB of the Periodic Table of the Elements. In particular,when a lower quality gas well condensate is used that contains up to 0.7wt-% mercaptans, sulfides and disulfides, it is highly desirable toprocess this stream to reduce the sulfur compound level below 5 wppmthat is detrimental to the platinum catalyst used to make LAB. Thesulfur compounds may be removed by use of adsorbents known to one ofordinary skill in the art. Advantageous results can be found using anadsorbent bed comprising ADS-102, PEP adsorbent available from UOP LLC,Des Plaines, Ill.

The adsorbent bed may be exclusively dedicated to treating theparaffin-rich or olefin-rich paraffins stream or it may be integratedwith a chemical conversion process that uses the paraffins stream toeffect other separations. A dedicated adsorbent bed is one whereessentially its sole purpose is to remove oxygenates from the paraffinsstream regardless of whether only the paraffins stream passes through itor the paraffins stream is combined with a chemical conversion processstream and the combined stream passes through the bed. In an integratedadsorbent bed, the paraffins stream and a process stream are combinedand the adsorbent bed serves to remove at least one component in theprocess stream. For example, in processes for alkylation process formaking alkyl benzenes from paraffins, paraffins are dehydrogenated, andthe dehydrogenation stream is typically passed through an adsorbent bedsuch as zeolite 13× to remove undesirable aromatics. In such processes,the paraffins stream is preferably fed to the process afterdehydrogenation and prior to the adsorption of water and aromatics inthe adsorption bed.

When dedicated, the adsorbent bed is typically operated at a temperaturebetween 25 to 60° C. and preferably is operated slightly above ambient(40° C.). While this adsorbent bed has been found to reduce the level ofoxygenates below the level that is measurable by gas chromatography,since it has been found that under some conditions these adsorbent bedsbecome less efficient over time in removal of the oxygenates furthermeasures are needed to insure that all oxygenates are removed.Accordingly, in the preferred embodiments of the invention, a secondadsorbent bed operating at an elevated temperature between about 150°and 200° C. containing a 5A adsorbent has been found to remove anyresidual oxygenates not removed by the first bed. Adsorbent beds thatare integrated with a process using the paraffin-rich or olefin-richparaffins stream are generally operated under conditions suitable forthe process.

After the adsorbent beds have reached their capacity for removal ofoxygenates from paraffin-rich streams, a regeneration procedure isfollowed to remove the adsorbed oxygenates from the adsorbent bed. A gasor liquid is sent through the bed, which is maintained at an elevatedtemperature for a sufficient period of time for the bed to berejuvenated through the removal of the oxygenates. In one embodiment ofthe rejuvenation process, nitrogen was used as the regenerant gas at3000 GHSV, the bed was first heated to 130° C. for two hours and thenthe temperature increased to 250° C. for three more hours. Otherregenerant gases or liquids may be used, such as available processstreams. The bed may also be regenerated in accordance with theprocedure set forth in U.S. Pat. No. 6,225,518 B1, incorporated hereinby reference in its entirety. Usually, due to the low concentration ofoxygenates, the integrated adsorbent bed is regenerated or replacedbased upon its performance in the process.

EXAMPLE

Laboratory tests have been made determine the extent of oxygenateremoval from hydrocarbons. The process is carried out in a 20 mlstainless steel column. The column is installed in an enclosed box andis packed with 20 ml of adsorbent. Initially, the temperature of theenclosed box is raised to the desired temperature, which was 40° C. inthis example. After stabilizing the temperature, oxygenate-containinghydrocarbon feed is introduced with a flow rate of 4 LHSV. The effluentis collected and analyzed for the oxygenate impurities. The feed thatwas tested contained 1000 ppm each of five typical kerosene containingoxygenates: 2-undecanone, 2-undecanol, decyl alcohol, lauric acid, and2-dodecanol. Very sharp breakthroughs were noted with alumina, silicagel, and sodium X types of adsorbents. In FIG. 1, the alumina tested asan adsorbent was a spherical promoted alumina, sold by UOP LLC, DesPlaines, Ill. as 9139A activated alumina. The adsorbent had a capacityof 21.95 wt-%. In FIG. 2, the adsorbent was Eagle 32-950 silica gel,sold by Eagle Chemical Co, Inc., Mobile, Ala. The adsorbent had acapacity of 19.76 wt-%. In FIG. 3, the adsorbent used was silica gelGrace 408, sold by W. R. Grace, Grace Davison division, Columbia, Md.The adsorbent had a capacity of 32.33 wt-%. In FIG. 4, Molsiv adsorbentMRG-E is used and is sold by UOP, Des Plaines, Ill. The adsorbent had acapacity of 23.57 wt-%. Each of the figures shows the substantialcapacity of these adsorbents for the oxygenates, along with a sharpbreakthrough after the capacity of the adsorbent has been achieved.Also, it is noted that lauric acid is strongly adsorbed by the adsorbentin all four cases.

1. A process for alkylation of olefins comprising: a) first sending afeed stream comprising 50 to 99.99 wt-% C10 to C15 paraffins and up to50 wt-% olefins through at least one adsorbent bed comprising one ormore adsorbents selected from the group consisting of alkaline oralkaline earth cation exchange X-zeolite wherein said adsorbents removeessentially all hydrocarbon oxygenates from said stream by adsorption;b) then combining said stream with benzene to form an alkylation stream;and c) alkylating said olefins by passing the alkylation stream to areactor containing an alkylation catalyst to convert at least a portionof said alkylation stream to alkylated benzene; wherein the process foralkylation further comprises the dehydrogenation of paraffins, removalof any aromatics contained within said feed stream in an adsorption bedand reaction of the dehydrogenated paraffin with benzene, and whereinthe adsorbent bed for the removal of oxygenates comprises an adsorbentbed for removal of aromatics.
 2. The process of claim 1 wherein aftersaid paraffins pass through said adsorbent bed, said paraffins are sentto a second adsorbent bed comprising 5A zeolite adsorbent to furtherremove oxygenates.
 3. The process of claim 1 wherein a dehydrogenatedstream is fed to the process for alkylation subsequent to thedehydrogenation and prior to the removal of aromatics in the adsorbentbed.